The present invention relates to a solar telescope and more particularly to a folded-path telescope for projecting an image of the sun that can be easily aimed at the sun.
Observing the sun using a telescope is fraught with difficulty. Direct vision can risk eye damage. Solar filters are often added to astronomical telescopes. These can fall off or crack due to the sun""s heat, exposing the viewer""s eye to the concentrated rays of the sun. In addition, astronomical telescopes are often large, unwieldy, hard to point and optimized for viewing dim objects at night. It is desirable to have a small, easy to use telescope that is as safe as possible. A telescope that can project a solar image onto a viewing surface allows users to observe sunspots and sketch drawings of the projected solar image onto a removable writing surface placed on the viewing surface.
A device is described in U.S. Pat. No. 4,437,736 wherein the sun viewing apparatus is a self-contained device consisting of a light shield with an aperture for admitting the rays of the sun and a series of pre-aligned lenses and prisms to display an image of the sun on a screen to reduce the threat of eye damage. This device suffers from difficulty in aligning the telescope with the sun and maintaining instrument alignment as the sun moves across the sky. In general, the sun moves through its own diameter across the sky in about two minutes, so frequent readjustment of the device is necessary to maintain a projected solar image. Adjusting the telescope alignment should be simple and easy to accomplish. However, this device does not provide simple means or methods for adjusting the telescope to the proper orientation for solar observation. Generally props must be placed beneath a corner of the instrument to tilt the telescope to the proper position in order to project an image of the sun.
Mounting systems for supporting a telescope are disclosed in U.S. Pat. No. Des. 247,854 wherein a portion of the telescope is in the form of a sphere that rests on a curved mount such that friction between the curved mount and the spherical telescope maintains the telescope orientation. The cylindrical portion of the telescope, which extends from the sphere, shifts the balance point of the telescope such that a significant amount of force is required to overcome the stabilizing friction to adjust the alignment of the telescope.
Another telescope and telescope support device is disclosed in U.S. Pat. No. 4,470,672 that describes a telescope with a large external ring attached to the side and end of a telescope, which acts as a mounting system for attachment of the telescope to a support. With the center of gravity adjusted to be close to the middle of the ring, the telescope is supposed to remain at a specified position at any azimuth or elevation. However, because the telescope center of mass is not located at the origin of the support ring additional mechanical devices are necessary to stabilize the telescope at certain elevations. The elevation of the telescope is maintained by friction. However, since the location of the telescope center of mass is variable depending on telescope elevation, the amount of stabilizing force e.g. friction necessary to maintain a specified elevation varies. Spring-loaded adjusters or other mechanical devices are disclosed to provide variable amounts of friction between the mounting ring and the telescope support device, sufficient to stabilize the telescope orientation. This system is complex; involving a large number of pieces and several adjustment points that increase the cost of the telescope, telescope size and the level of difficulty in using the telescope.
There is a need for a solar telescope that can be quickly and easily aligned with the sun such that an image of the sun is readily projected to a viewing screen. In addition, the telescope should have a support system that facilitates alignment and provides sufficient stability regardless of azimuth or elevation of the telescope.
The present invention features a solar telescope that facilitates safe observation of the sun with minimal setup, targeting effort or operator skill. The folded solar telescope of the invention includes a support system for controlling telescope elevation such that the center of gravity of the telescope and the origin of the circle described by the arc of the curved support device are substantially coincident. The telescope further includes a targeting system that comprises one or more pointing aids where multiple pointing aids have a variety of sensitivities to telescope alignment. Sequential application of pointing aids with increasing sensitivity to telescope alignment simplifies the target acquisition process, so that an image of the target (e.g. the sun) is projected onto a viewing surface by the telescope.
In specific embodiments, a folded solar telescope of the invention is housed in a frame whose shape is described by a regular n-sided polygon, where n is an integer greater than 2, such as an equilateral triangle, a square, and the like. The telescope comprises an objective lens, two or more mirrors or prisms to fold the path of the light, an xe2x80x9ceyepiecexe2x80x9d lens and a viewing screen. The telescope components are suitably mounted on the telescope frame or on braces or other support objects that are mounted to the telescope frame.
The regular polygonal telescope frame rests on a curved telescope support device where preferably the curvature of the support device""s curved surface is defined by an arc of the circle that inscribes the regular polygon of the telescope frame. Preferably, the center of mass of the telescope is substantially coincident with the geometric center of the n-sided regular polygonal telescope frame. Further the center of mass of the telescope is substantially coincident with the origin of the circle that describes the curvature of the curved telescope support device because the origin of this circle is coincident to the center of the regular polygon of the telescope frame. The telescope""s center of mass is substantially located at an energy minimum for any elevation of the telescope from 0 to 90, thereby minimizing or eliminating rotational strain or torque on the telescope at virtually any telescope elevation. Consequently, a small amount of friction inherent to the contact between two or more apexes of the polygonal telescope frame with the curved surface of the telescope support device is sufficient to stabilize the telescope at a specified elevation. Additional stabilization aids such as clamps, spring rollers or other mechanical fasteners or tensioners are not required. Adjustment of the telescope elevation is simple to effect by overcoming the small amount of inherent static friction without the need for releasing or manipulating one or more stabilizing fasteners or tensioners.
The angular size of the sun is approximately xc2xd and pointing an instrument with a field of view of this size can be difficult. The present invention further includes a targeting system with one or more pointing aids to assist in adjusting the alignment of the telescope such that an object (e.g. the sun) is projected onto a viewing surface. The aiming process includes first pointing the telescope aperture and objective lens in the general direction of the sun. Additional telescope adjustment can include refining the alignment using a gnomon that is parallel to the axis defined by the center of the objective lens and the center of the first mirror or prism used for folding the path of the sun""s rays. Minimizing or eliminating the shadow cast by the gnomon brings the telescope into closer alignment with the target e.g. the sun. More sensitive telescope orientation refinement can further include using a pointing target assembly where a secondary aperture and a target define an axis parallel to the axis defined by the center of the objective lens and the center of the first mirror or prism for folding the path of the sun""s rays. Localizing the light rays from the secondary aperture onto the target brings the telescope further into alignment with the target e.g. the sun. The pointing target assembly is generally a more accurate targeting device than a gnomon. Preferred telescope alignment involves sequential orientation refinement steps with both a gnomon and a pointing target assembly to align the telescope with the sun to facilitate the projection of a solar image onto a viewing screen or surface.
In preferred embodiments, a gnomon or other geometrically regular object with one long dimension can be attached to the exterior of the telescope frame such that the gnomon is parallel to the axis defined by the center of the objective lens and the first mirror or prism. Preferably the long dimension of the gnomon or other regular object is parallel to the axis defined by the objective lens and the first mirror or prism. Adjusting the telescope orientation to eliminate the shadow cast by the gnomon brings the telescope into better alignment with the sun.
Preferred telescopes further comprise a second, more sensitive targeting assembly. A second aperture with a relatively small diameter is located in close proximity to the primary telescope aperture on the telescope frame. Additionally, the telescope has a pointing target mounted within the interior of the telescope frame. The pointing target is located so the line between the center of the target and the center of the second aperture is substantially parallel to the axis defined by the primary aperture and the first light-folding component e.g. mirror or prism. Localizing the light beam from the second aperture on the pointing target causes the light passing through the objective lens to contact the first light-folding mirror bringing the telescope into closer alignment with the target e.g. the sun.
For telescopes that include both a gnomon and a pointing target orienting apparatus, the distance between the second small aperture and the pointing target is preferably between 2 and 20 times the length of the gnomon. More preferably the distance is between about 4 and 12 times the length of the gnomon. Consequently the sensitivity of the pointing target pointing aid is more sensitive than the gnomon pointing aid by a factor of about 2 to about 8.
In additional embodiments, targeting methods are included whereby the elevation and azimuth of the telescope are adjusted according to one or more targeting steps to facilitate image acquisition of a specified target, e.g. the sun. The first rough telescope orientation is to set the approximate azimuth by orienting the telescope so that the frame is pointing towards the target. The first refinement is accomplished by adjusting the elevation and azimuth of the telescope so that the shadow cast by a gnomon is minimized or preferably eliminated. Additional, more sensitive refinement of the telescope orientation is accomplished by adjusting the elevation and azimuth of the telescope so that the beam of light passing through the second small aperture strikes the center of the pointing target. The pointing target based telescope orientation adjustment is about 2 to 8 times more sensitive than the gnomon-based adjustment. Preferably the pointing target refinement is about 3 to 5 times more sensitive than the gnomon-based adjustment. Final telescope orientation is accomplished by centering the target image, e.g. an image of the sun, on the viewing surface.
It is the object of this invention to provide a simple device that allows adults and children to more safely view the sun with a minimum of set-up time or adjustment. Further, the device is inexpensive to build, easy to maintain and optimized to solar viewing conditions.